1. Field of the Invention
The present invention relates to telephone receiver inserts, generally comprising a case containing a vibrating element for transforming into sound vibrations the electric signals conveyed to its input terminals by a supply line.
In the transducers used at present for telephony reception, the vibrating element is formed of a membrane held in position by its periphery in an insert case. The case comprises a base body with a central cavity whose periphery forms a bearing surface for the periphery of the vibrating membrane; the case further comprises a cover connected by its periphery to the base body and including an inner recess communicating with the outside through at least one orifice; the periphery of the cover comprises an inner annular relief bearing on the periphery of the membrane for holding it applied against the periphery of the cavity of the base body.
The central cavity of the base body defines, with the vibrating membrane, an inner base cavity. The inner cover recess defines, with the vibrating membrane, an inner cover cavity. The shape and dimensions of the inner base and cover cavities contributes substantially to determining the acoustic qualities of the insert.
Furthermore, the hearing aids for the hard of hearing are designed to amplify the acoustic vibrations received to make them perceptible to the ear. However, certain aids comprise an adjusting device which, in position "T", adapts them for picking up a magnetic field. These aids thus make correct operation possible when the transducer is of the electromagnetic type.
On the other hand, the magnetic field radiated by the coil of an electrodynamic sensor is limited, even insufficient, for ensuring the correct operation of a hearing aid. This drawback is noticeable with piezoelectric sensors, such sensors producing no magnetic field able to act on the magnetic field sensitive aids.
To overcome this drawback, telephone receiver inserts have been designed comprising auxiliary coils, fed by the electric signal controlling the vibrating membrane, and producing an auxiliary magnetic field able to be picked up by the hearing aids.
2. Description of the Prior Art
Such a solution is described for example in the patent FR-A-2 571581 in the name of the Applicant. The solution described in this patent however requires the provision of special inserts, comprising simultaneously the usual vibrating members of an insert and the magnetic field production members. Thus, if it is desired to have a telephone set compatible with the hearing aids sensitive to the magnetic field, it is necessary to completely change the electroacoustic insert to fit an insert described in this patent.
The document DE-U-8 715 846 describes a piezoelectric insert on which a coil body may be fixed forming a distinct assembly of the insert. The coil body has an annular shape which is fitted to a cylindrical part of the insert case. The coil body comprises housings in which coil connectors are disposed forming the end of the coil winding. When the coil body is engaged on the insert case, the insert connectors penetrate progressively inside the housings of the coil body. At the end of engagement, the insert connectors are disposed entirely inside housings in the coil body, and come close to the coil connectors. Resilient added tags assemble and connect together the insert connectors and the coil connectors. Thus, in this document the addition of the coil and its connection require added resilient tags which form additional parts. Considering the small size of the housings, fitting is relatively difficult and complicates assembly. On the other hand, the method of coupling the coil to the insert body imposes a special geometrical shape on the receiver insert. The result is that a family of inserts of different diameters requires a corresponding family of coils of different diameters. The type of connection, provided by an additional part, introduces contact impedances in the main electric circuit of the insert and there is a danger of disturbing its operation following the fitting of a coil.